1. Field of the Invention
The present invention relates to an image forming apparatus, and more specifically to an image forming apparatus that requires regular head maintenance, such as an inkjet recording apparatus that performs printing to form an image by ejecting ink from an ink ejection head, in which maintenance of the head can be performed during printing.
2. Description of the Related Art
Conventionally, one known example of an image forming apparatus is an inkjet recording apparatus (inkjet printer) that has an inkjet head (ink ejection head) with an alignment of multiple nozzles and that forms an image on a recording medium by ejecting ink from the nozzles while moving the inkjet head and the recording medium relative to each other.
Various methods are known in conventional practice as ink ejection methods for such an inkjet recording apparatus. Known examples include a piezoelectric system wherein a vibration plate that constitutes part of a pressure chamber (ink chamber) is deformed by the deformation of a piezoelectric element (piezoelectric ceramic), the capacity of the pressure chamber is changed, ink is led into the pressure chamber from an ink supply channel during this increase in pressure chamber capacity, and the ink in the pressure chamber is ejected as droplets during the decrease in pressure chamber capacity. Further, known examples also include a thermal inkjet system wherein ink is heated to create air bubbles for ejecting the ink by the expansion energy when the air bubbles grow.
In an image forming apparatus that has an ink ejection head, such as an inkjet recording apparatus, ink is supplied from an ink tank that stores ink to an ink ejection head via an ink supply channel, and the ink is ejected by the ejection methods described above. The ink used herein is preferably dried and fixed immediately upon being ejected onto the recording medium.
Since ink always fills the nozzles of the ink ejection head so that printing can be immediately carried out when a print command is received, and ink ejection of ink from the nozzles becomes unstable when the ink in the nozzles dries, the ink ejection head is sealed with a cap to ensure that the ink in the nozzles does not dry during standby.
However, in the nozzles which do not eject the ink for a long time during printing, since the ink in the nozzles is exposed to the air, the drying and the viscosity of ink in the nozzles is increased. Therefore, since the nozzles become clogged or have no ink for ejecting, there is a problem to hinder the ink from being ejecting. In order to solve the problem, a purging operation must be performed to forcefully eject the ink from the nozzles at regular intervals.
When air bubbles that are mixed in the ink supply channel and the like accumulate in the ink ejection head or in front of the filter for removing impurities from the ink supply channel, ink cannot be ejected from the nozzles. Therefore, there is a problem to block ink from supplying by the accumulated air bubbles.
Furthermore, when ejection continues over an extended period, the refill of ink is slowed, nozzle pressure becomes too low, and ink ejection becomes unstable. Therefore the nozzle pressure must be periodically reset to its initial state by suctioning the ink from the nozzles with a pump.
Staining of the nozzle surface by splashes or by the ejected ink ricocheting off the printing surface may be the cause of ejection failure or the like, therefore the nozzle surface must be periodically cleaned by using a blade on (wiping) the nozzle surface.
In order to deal with such causes of ink ejection failure in an inkjet recording apparatus, various methods have been proposed in conventional practice.
One known example of a piezoelectric inkjet recording apparatus is an apparatus wherein ink in the ink chamber is made to oscillate by applying an AC electric field to the piezoelectric oscillator of the dot for which not ink is ejected during recording (during printing), and the ink in the ink chamber is made to flow to prevent the ink from drying (for example, see Japanese Patent Application Publication No. 9-290505).
Another example is one wherein a conveyor belt for conveying the recording paper is provided with a plurality of ports at specific intervals in the direction in which the recording paper is conveyed (for example, see Japanese Patent Application Publication No. 2001-113690). In the inkjet recording apparatus, the ink is ejected from the print head to each of the plurality of ports during printing, and the ejected ink is recovered via the conveyor belt by a recovery mechanism device disposed so as to face the print head. Therefore, a purging operation is performed during printing.
Yet another example is one having a line head with a plurality of nozzles disposed along a length equivalent to the width of the recording medium, wherein an auxiliary head with an image recording width equal to or greater than the image recording width of the line head, or an auxiliary head capable of moving in the line direction of the line head, is in parallel alignment with the line head (for example, see Japanese Patent Application Publication No. 11-334047). When the nozzles in the line head have a defect, the image is formed by using the auxiliary head aligned parallel to the line head.
Furthermore, still another example is one having a linear recording head and a serial recording head capable of moving in the direction that the nozzles are aligned in the linear recording head (for example, see Japanese Patent Application Publication No. 2-276647). When nozzles incapable of ejecting ink are detected in the linear recording head, the location of these nozzles is recorded by the serial recording head.
However, the example disclosed in Japanese Patent Application Publication No. 9-290505 has the effect of preventing the ink in the nozzles from increasing in viscosity or solidifying during printing, but ink cannot be suctioned and the nozzle surface cannot be cleaned with a blade during printing.
In the example disclosed in Japanese Patent Application Publication No. 2001-113690, the purging operation can be performed during printing, but ink cannot be suctioned and the nozzle surface cannot be cleaned with a blade during printing.
The example disclosed in Japanese Patent Application Publication No. 11-334047 is not configured so that the recovery processing can be performed on the nozzles in the main line head incapable of ejecting ink while the auxiliary head is being used for ejecting.
The example disclosed in Japanese Patent Application Publication No. 2-276647 is not configured so that the recovery processing can be performed on the main linear recording head while the auxiliary head (serial recording head) is being used for ejecting. In addition, the auxiliary head disclosed in Japanese Patent Application Publication No. 2-276647 has one nozzle, and images cannot be formed without the main linear recording head by merely compensating for the omission of dots by the nozzles in the main linear recording head incapable of ejecting ink.
Therefore, there are conventional problems in which neither a purging operation for removing the cause of such ejection failures previously described, nor head maintenance operations such as suction and cleaning with a blade can be performed during printing by placing the recording medium directly underneath the head during printing, when using a line head in which only a number of nozzles corresponding to the entire width of the recording medium are aligned in a line configuration in the width direction of the recording medium.